Historically, most oil and gas reservoirs have been developed and managed under timetables and scenarios as follows: a preliminary investigation of an area was conducted using broad geological methods for collection and analysis of data such as seismic, gravimetric, and magnetic data, to determine regional geology and subsurface reservoir structure. In some instances, more detailed seismic mapping of a specific structure was conducted in an effort to reduce the high cost, and the high risk, of an exploration well. A test well was then drilled to penetrate the identified structure to confirm the presence of hydrocarbons, and to test productivity. In lower-cost onshore areas, development of a field would commence immediately by completing the test well as a production well. In higher cost or more hostile environments such as the North Sea, a period of appraisal would follow, leading to a decision as to whether or not to develop the project. In either case, based on inevitably sparse data, further development wells, both producers and injectors would be planned in accordance with a reservoir development plan. Once production and/or injection began, more dynamic data would become available, thus, allowing the engineers and geoscientists to better understand how the reservoir rock was distributed and how the fluids were flowing. As more data became available, an improved understanding of the reservoir was used to adjust the reservoir development plan resulting in the familiar pattern of recompletion, sidetracks, infill drilling, well abandonment, etc. Unfortunately, not until the time at which the field was abandoned, and when the information is the least useful, did reservoir understanding reach its maximum.
Limited and relatively poor quality of reservoir data throughout the life of the reservoir, coupled with the relatively high cost of most types of well intervention, implies that reservoir management is as much an art as a science. Engineers and geoscientists responsible for reservoir management discussed injection water, fingering, oil-water contacts rising, and fluids moving as if these were a precise process. The reality, however, is that water expected to take three years to break through to a producing well might arrive in six months in one reservoir but might never appear in another. Text book “piston like” displacement rarely happens, and one could only guess at flood patterns.
For some time, reservoir engineers and geoscientists have made assessments of reservoir characteristics and optimized production using down hole test data taken at selected intervals. Such data usually includes traditional pressure, temperature and flow data is well known in the art. Reservoir engineers have also had access to production data for the individual wells in a reservoir. Such data as oil, water and gas flow rates are generally obtained by selectively testing production from the selected well at selected intervals.
Recent improvements in the state of the art regarding data gathering, both down hole and at the surface, have dramatically increased the quantity and quality of data gathered. Examples of such state of the art improvements in data acquisition technology include assemblies run in the casing string comprising a sensor probe with optional flow ports that allow fluid inflow from the formation into the casing while sensing wellbore and/or reservoir characteristics as described and disclosed in international PCT application WO. 97/49894, assigned to Baker Hughes, the disclosure of which is incorporated herein by reference. The casing assembly may further include a microprocessor, a transmitting device, and a controlling device located in the casing string for processing and transmitting real time data. A memory device may also be provided for recording data relating to the monitored wellbore or reservoir characteristics. Examples of down hole characteristics which may be monitored with such equipment include: temperature, pressure, fluid flow rate and type, formation resistivity, cross-well and acoustic seismometry, perforation depth, fluid characteristics and logging data. Using a microprocessor, hydrocarbon production performance may be enhanced by activating local operations in additional downhole equipment. A similar type of casing assembly used for gathering data is described and illustrated in international PCT application WO 98/12417, assigned to BP Exploration Operating Company Limited, the disclosure of which is incorporated by reference.
Recent technology improvements in downhole flow control devices are disclosed in UK Patent Application GB 2,320,731A which describes a number of downhole flow control devices which may be used to shut off particular zones by using downhole electronics and programing with decision making capacity, the disclosure of which is incorporated by reference.
Another important emerging technology that may have a substantial impact on managing reservoirs is time lapsed seismic, often referred to a 4-D seismic processing. In the past, seismic surveys were conducted only for exploration purposes. However, incremental differences in seismic data gathered over time are becoming useful as a reservoir management tool to potentially detect dynamic reservoir fluid movement. This is accomplished by removing the non-time varying geologic seismic elements to produce a direct image of the time-varying changes caused by fluid flow in the reservoir. By using 4-D seismic processing, reservoir engineers can locate bypassed oil to optimize infill drilling and flood pattern. Additionally, 4-D seismic processing can be used to enhance the reservoir model and history match flow simulations.
International PCT application WO 98/07049, assigned to Geo-Services, the disclosure of which is incorporated herein by reference, describes and discloses state of the art seismic technology applicable for gathering data relevant to a producing reservoir. The publication discloses a reservoir monitoring system comprising: a plurality of permanently coupled remote sensor nodes, wherein each node comprises a plurality of seismic sensors and a digitizer for analog signals; a concentrator of signals received from the plurality of permanently coupled remote sensor nodes; a plurality of remote transmission lines which independently connect each of the plurality of remote sensor nodes to the concentrator, a recorder of the concentrated signals from the concentrator, and a transmission line which connects the concentrator to the recorder. The system is used to transmit remote data signals independently from each node of the plurality of permanently coupled remote sensor nodes to a concentrator and then transmit the concentrated data signals to a recorder. Such advanced systems of gathering seismic data may be used in the reservoir management system of the present invention as disclosed hereinafter in the Detailed Description section of the application.
Historically, down hole data and surface production data has been analyzed by pressure transient and production analysis. Presently, a number of commercially available computer programs such as Saphir and PTA are available to do such an analysis. The pressure transient analysis generates output data well known in the art, such as permeability-feet, skin, average reservoir pressure and the estimated reservoir boundaries. Such reservoir parameters may be used in the reservoir management system of the present invention.
In the past and present, geoscientists, geologists and geophysicists (sometimes in conjunction with reservoir engineers) analyzed well log data, core data and SDL data. The data was and may currently be processed in log processing/interpretation programs that are commercially available, such as Petroworks and DPP. Seismic data may be processed in programs such as Seisworks and then the log data and seismic data are processed together and geostatistics applied to create a geocellular model.
Presently, reservoir engineers may use reservoir simulators such as VIP or Eclipse to analyze the reservoir. Nodal analysis programs such as WEM, Prosper and Openflow have been-used in conjunction with material balance programs and economic analysis programs such as Aries and ResEV to generate a desired field wide production forecast. Once the field wide production has been forecasted, selected wells may be produced at selected rates to obtain the selected forecast rate. Likewise, such analysis is used to determine field wide injection rates for maintenance of reservoir pressure and for water flood pattern development. In a similar manner, target injection rates and zonal profiles are determined to obtain the field wide injection rates.
It is estimated that between fifty and seventy percent of a reservoir engineer's time is spent manipulating data for use by each of the computer programs in order for the data gathered and processed by the disparate programs (developed by different companies) to obtain a resultant output desired field wide production forecast. Due to the complexity and time required to perform these functions, frequently an abbreviated incomplete analysis is performed with the output used to adjust a surface choke or recomplete a well for better reservoir performance without knowledge of how such adjustment will affect reservoir management as a whole.